Raman spectroscopic apparatus, raman spectroscopic method, and electronic apparatus

ABSTRACT

A Raman spectroscopic apparatus analyzes a substance under analysis and includes a light source that emits light of a first wavelength, an optical device that adsorbs the substance under analysis and is irradiated with the light of the first wavelength, and an optical detector that receives light radiated from the optical device. The optical device includes a first structural member that generates charge transfer resonance in response to the light of the first wavelength and a second structural member that is less than or equal to 5 nm from the first structural member and generates surface plasmon resonance in response to the light of the first wavelength. The first structural member is made of a metal or a semiconductor, and the second structural member is made of a metal different from the material of the first structural member.

BACKGROUND

1. Technical Field

The present invention relates to a Raman spectroscopic apparatus, aRaman spectroscopic method, and an electronic apparatus.

2. Related Art

In recent years, the demand for a sensor chip (optical device) used formedical diagnosis, beverage and food inspection, and other purposes hasbeen increasing, and the development of a highly sensitive, compactsensor chip has been desired. To meet the demand, sensor chips of avariety of types including a sensor chip using an electrochemicalapproach have been studied. Among them, a sensor chip usingspectroscopic analysis based on surface plasmon resonance (SPR), inparticular, surface enhanced Raman scattering (SERS) has receivedincreasing attention for a variety of reasons. For example, such asensor chip can be an integrated chip, can be manufactured at low cost,and can be used in any measurement environment.

Surface plasmon is a vibration mode of an electron wave that is coupledto light under certain surface-specific boundary conditions. To excitesurface plasmon, there are a method in which a diffraction gratingengraved on a metal surface is used to couple light and plasmon to eachother and a method in which an evanescent wave is used. An example of asensor chip using SPR is formed of a total reflection prism and a metalfilm that is formed on a surface of the prism and comes into contactwith a target substance. The thus configured sensor chip detects whetheror not a target substance has been adsorbed, for example, whether or notan antigen in an antigen-antibody reaction has been adsorbed.

There is propagating surface plasmon present on a metal surface, whereasthere is localized surface plasmon present on a metal fine particle. Itis understood that when the localized surface plasmon, that is, surfaceplasmon localized on a metal microstructure of a surface is excited, asignificantly enhanced electric field is induced.

It is further understood that when an enhanced electric field formed bylocalized surface plasmon resonance (LSPR) using metal nano-particles isirradiated with Raman scattered light, a surface enhanced Ramanscattering phenomenon enhances the Raman scattered light, and a highlysensitive sensor (detection device) has been proposed. Using theprinciple described above allows detection of trace quantities of avariety of substances.

For example, JP-A-2013-96939 describes a Raman spectroscopic apparatusincluding a sensor chip in which metal particles made of Ag or Au areperiodically arranged.

However, the Raman spectroscopic apparatus described in JP-A-2013-96939,which has a trap film, cannot detect every target substance in a highlysensitive manner. Further, for example, a Raman spectroscopic apparatusincluding a sensor chip (optical device) in which metal particles madeof Ag are periodically arranged can detect a molecule containing an Natom having an unpaired electron, such as pyridine and adenine, in ahighly sensitive manner because Ag tends to chemically adsorb such amolecule but cannot detect a molecule not containing an N atom, such asacetone and ethanol, in a highly sensitive manner because Ag does nottend to chemically adsorb such a molecule.

SUMMARY

An advantage of some aspects of the invention is to provide a Ramanspectroscopic apparatus capable of detecting Raman scattered light froma target substance in a highly sensitive manner. Another advantage ofsome aspects of the invention is to provide a Raman spectroscopic methodthat allows detection of Raman scattered light from a target substancein a highly sensitive manner. Still another advantage of some aspects ofthe invention is to provide an electronic apparatus including the Ramanspectroscopic apparatus described above.

An aspect of the invention is directed to a Raman spectroscopicapparatus that analyzes a substance under analysis (target substance)and includes a light source that emits light of a first wavelength, anoptical device that adsorbs the substance under analysis (targetsubstance) and is irradiated with the light of the first wavelength, andan optical detector that receives light radiated from the opticaldevice, wherein the optical device includes a first structural memberthat generates charge transfer resonance in response to the light of thefirst wavelength, and a second structural member that is disposed in aposition spaced apart from the first structural member by a spacing lessthan or equal to 5 nm and generates surface plasmon resonance inresponse to the light of the first wavelength, the first structuralmember is made of a metal or a semiconductor, and the second structuralmember is made of a metal different from the material of the firststructural member.

The Raman spectroscopic apparatus described above can provide a chemicalenhancement effect even when the substance under analysis (targetsubstance) is acetone or ethanol, which a Raman spectroscopic apparatusincluding an optical device having periodically arranged metal particlesmade of, for example, Ag cannot detect in a highly sensitive manner, andthe resultant synergy between an electric field enhancement effect andthe chemical enhancement effect allows a SERS effect to be provided. Asa result, the Raman spectroscopic apparatus described above can increasethe intensity of Raman scattered light and can hence detect Ramanscattered light from the substance under analysis (target substance) ina highly sensitive manner.

In the Raman spectroscopic apparatus according to the aspect of theinvention, the first structural member may be provided so that the firststructural member coats the second structural member.

In the Raman spectroscopic apparatus described above, the optical devicecan be formed in simpler manufacturing steps.

In the Raman spectroscopic apparatus according to the aspect of theinvention, the first structural member may be provided in a plurality ofpositions, the second structural member may be provided in a pluralityof positions, and the plurality of second structural members may bespaced apart from each other.

In the Raman spectroscopic apparatus described above, the optical devicecan be formed in simpler manufacturing steps, and the electric fieldenhancement effect can be enhanced.

In the Raman spectroscopic apparatus according to the aspect of theinvention, the plurality of first structural members may be spaced apartfrom each other.

The Raman spectroscopic apparatus described above can detect Ramanscattered light from the substance under analysis (target substance) ina highly sensitive manner.

In the Raman spectroscopic apparatus according to the aspect of theinvention, the first structural member may have a thickness less than orequal to 1 nm.

In the Raman spectroscopic apparatus described above, the electric fieldenhancement effect can be enhanced.

In the Raman spectroscopic apparatus according to the aspect of theinvention, the second structural member may be made of Ag, Au, or Al.

In the Raman spectroscopic apparatus described above, each of Ag, Au,and Al is a metal having a dielectric constant with a small imaginarypart in the visible wavelength range and can hence enhance the electricfield enhancement effect.

In the Raman spectroscopic apparatus according to the aspect of theinvention, the substance under analysis (target substance) may beacetone or ethanol.

The Raman spectroscopic apparatus described above can also detect amolecule not containing an N atom, such as acetone and ethanol, in ahighly sensitive manner.

In the Raman spectroscopic apparatus according to the aspect of theinvention, the substance under analysis (target substance) may beacetone, the first wavelength may be greater than or equal to 500 nm butless than or equal to 700 nm, and the second structural member may havea size greater than or equal to 40 nm but less than or equal to 75 nm.

The Raman spectroscopic apparatus described above allows the wavelengthband where the electric field enhancement effect can be enhanced and thewavelength band where the chemical enhancement effect can be enhanced tocoincide with each other. As a result, synergy between the electricfield enhancement effect and the chemical enhancement effect can be morereliably obtained.

The Raman spectroscopic apparatus according to the aspect of theinvention may further include a light source that irradiates thesubstance under analysis (target substance) with light of a secondwavelength having energy corresponding to the difference in energybetween a ground state and a minimally excited state of the substanceunder analysis (target substance).

In the Raman spectroscopic apparatus described above, the reaction inwhich the first structural member adsorbs the substance under analysis(target substance) is encouraged, whereby the chemical enhancementeffect can be enhanced.

Another aspect of the invention is directed to a Raman spectroscopicmethod including irradiating an optical device that adsorbs a substanceunder analysis (target substance) with light of a first wavelength andreceiving light radiated from the optical device for analysis of thesubstance under analysis (target substance), wherein the optical deviceincludes a first structural member that generates charge transferresonance in response to the light of the first wavelength, and a secondstructural member that is disposed in a position spaced apart from thefirst structural member by a spacing less than or equal to 5 nm andgenerates surface plasmon resonance in response to the light of thefirst wavelength, the first structural member is made of a metal or asemiconductor, and the second structural member is made of a metaldifferent from the material of the first structural member.

The Raman spectroscopic method described above allows highly sensitivedetection of Raman scattered light from the substance under analysis(target substance).

Still another aspect of the invention is directed to an electronicapparatus including the Raman spectroscopic apparatus according to theaspect of the invention, a computation unit that computes health careinformation based on detected information from the optical detector, astorage unit that stores the health care information, and a display unitthat displays the health care information.

The electronic apparatus described above, which includes the Ramanspectroscopic apparatus according to the aspect of the invention, canreadily detect a trace quantity of substance and provide highly precisehealth care information.

In the electronic apparatus according to the aspect of the invention,the health care information may include information on whether or notthere is at least one type of biological substance selected from thegroup including bacteria, viruses, proteins, nucleic acids, and antigensand antibodies or at least one type of compound selected from inorganicmolecules and organic molecules or information on the amount thereof.

The electronic apparatus described above can readily detect a tracequantity of substance and provide highly precise health careinformation.

Yet another aspect of the invention is directed to a Raman spectroscopicapparatus that analyzes a substance under analysis (target substance)and includes a light source that emits light of a first wavelength, anoptical device that adsorbs the substance under analysis (targetsubstance) and is irradiated with the light of the first wavelength, andan optical detector that receives light radiated from the opticaldevice, wherein the optical device includes a substrate, a firststructural member that is formed on the substrate and generates chargetransfer resonance in response to the light of the first wavelength, anda second structural member that is formed on the substrate, is disposedin a position spaced apart from the first structural member by a spacingless than or equal to 5 nm, and generates surface plasmon resonance inresponse to the light of the first wavelength, the first structuralmember is made of a metal or a semiconductor, and the second structuralmember is made of a metal different from the material of the firststructural member.

The Raman spectroscopic apparatus described above can provide thechemical enhancement effect even when the substance under analysis(target substance) is acetone or ethanol, which a Raman spectroscopicapparatus including an optical device having periodically arranged metalparticles made of, for example, Ag cannot detect in a highly sensitivemanner, and the resultant synergy between the electric field enhancementeffect and the chemical enhancement effect allows a SERS effect to beprovided. As a result, the Raman spectroscopic apparatus described abovecan increase the intensity of Raman scattered light and can hence detectRaman scattered light from the substance under analysis (targetsubstance) in a highly sensitive manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described with reference to theaccompanying drawings, wherein like numbers reference like elements.

FIG. 1 diagrammatically shows a Raman spectroscopic apparatus accordingto an embodiment of the invention.

FIG. 2 is a cross-sectional view diagrammatically showing an opticaldevice of the Raman spectroscopic apparatus according to the presentembodiment.

FIG. 3 describes charge transfer resonance.

FIG. 4 diagrammatically shows a specific configuration of the Ramanspectroscopic apparatus according to the present embodiment.

FIG. 5 diagrammatically shows an SDRS measurement system.

FIG. 6 shows SDRS spectra before and after pyridine vapor is exposed toan Ag surface.

FIG. 7 shows SDRS spectra before and after acetic acid vapor is exposedto the Ag surface.

FIG. 8 shows SDRS spectra before and after acetone vapor is exposed tothe Ag surface.

FIG. 9 shows SDRS spectra before and after ethanol vapor is exposed tothe Ag surface.

FIG. 10 shows SERS spectra in gas-state pyridine, acetic acid, acetone,and ethanol atmospheres in a case where an excitation wavelength is 632nm.

FIG. 11 shows a graph illustrating the relationship between theexcitation wavelength and SERS intensity in the gas-state acetic acidatmosphere.

FIG. 12 shows SDRS spectra before and after acetone vapor is exposed toan Al surface.

FIG. 13 shows a SERS spectrum in the gas-state acetone atmosphere in thecase where the excitation wavelength is 632 nm.

FIG. 14 is a SEM photograph of a specimen used in an experiment.

FIG. 15 shows graphs illustrating the relationship between theexcitation wavelength and optical density.

FIG. 16 is a cross-sectional view diagrammatically showing an opticaldevice of a Raman spectroscopic apparatus according to a first variationof the present embodiment.

FIG. 17 is a SEM photograph of an island-shaped Ag structure.

FIG. 18 shows graphs illustrating the relationship between Al thicknessand relative SERS intensity.

FIG. 19 is a cross-sectional view diagrammatically showing an opticaldevice of a Raman spectroscopic apparatus according to a secondvariation of the present embodiment.

FIG. 20A is a perspective view diagrammatically showing a step ofmanufacturing the Raman spectroscopic apparatus according to the secondvariation of the present embodiment, and FIG. 20B is a SEM photographshowing the manufacturing step.

FIG. 21A is a perspective view diagrammatically showing another step ofmanufacturing the Raman spectroscopic apparatus according to the secondvariation of the present embodiment, and FIG. 21B is a SEM photographshowing the manufacturing step.

FIG. 22A is a perspective view diagrammatically showing another step ofmanufacturing the Raman spectroscopic apparatus according to the secondvariation of the present embodiment, and FIG. 22B is a SEM photographshowing the manufacturing step.

FIG. 23 shows graphs illustrating the relationship between Al thicknessand relative SERS intensity.

FIG. 24 shows SDRS spectra before and after acetone vapor is exposed toan Si surface.

FIG. 25 describes how Si adsorbs acetone.

FIG. 26 diagrammatically shows a Raman spectroscopic apparatus accordingto a fourth variation of the present embodiment.

FIG. 27 describes the structure of an acetone molecule.

FIG. 28 shows an absorption spectrum of acetone gas alone in avisible-ultraviolet region.

FIG. 29 shows SDRS spectra before and after acetone vapor is exposed toa Cu surface.

FIG. 30 diagrammatically shows an electronic apparatus according to thepresent embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A preferred embodiment of the invention will be described below indetail with reference to the drawings. The embodiment that will bedescribed below is not intended to unduly limit the scope of theinvention set forth in the appended claims. Further, all theconfigurations that will be described below are not necessarilyessential configuration requirements of the invention.

1. RAMAN SPECTROSCOPIC APPARATUS

A Raman spectroscopic apparatus according to an embodiment of theinvention will first be described with reference to the drawings. FIG. 1diagrammatically shows a Raman spectroscopic apparatus 100 according tothe present embodiment.

The Raman spectroscopic apparatus 100 includes an optical device (sensorchip) 10, a light source 20, and an optical detector 30, as shown inFIG. 1. The Raman spectroscopic apparatus 100 detects and analyzes(qualitatively analyzes or quantitatively analyzes) Raman scatteredlight from a target substance. The optical device 10, the light source20, and the optical detector 30 will be sequentially described below.

1.1. Optical Device

FIG. 2 is a cross-sectional view diagrammatically showing the opticaldevice 10 of the Raman spectroscopic apparatus 100 according to thepresent embodiment. The optical device 10 includes a substrate 12, firststructural members 14, and second structural members 16, as shown inFIG. 2. The optical device 10 adsorbs a target substance and isirradiated with light L1 of a first wavelength emitted from the lightsource 20.

The substrate 12 is, for example, a glass substrate. Although not shown,a metal layer may be provided on the lower surface of the substrate 12.

The first structural members 14 are provided on the substrate 12. Theshape of the first structural members 14 is not limited to a specificshape, and the first structural members 14 in the example shown in FIG.2 have a semicircular cross-sectional shape. The structural members 14may have a circular shape in a plan view. The first structural members14 may instead have a cylindrical shape. The first structural members 14have a thickness, for example, greater than or equal to 0.5 nm but lessthan or equal to 30 nm. The first structural members 14 have a size (thesize in a plan view, the diameter in the case where the shape in a planview is a circle), for example, greater than or equal to 0.5 nm but lessthan or equal to 80 nm. The first structural members 14 are disposed ina plurality of positions in correspondence with the second structuralmembers 16. The spacing (e.g., distance) between adjacent firststructural members 14 is, for example, greater than or equal to 1 nm butless than or equal to 100 nm.

The first structural members 14 are made of a metal. The firststructural members 14 are preferably made of, for example, Al, Ag, Au,or Cu.

The first structural members 14 adsorb a target substance (targetmolecule) that is not shown. The term “adsorb” used herein is aphenomenon in which the concentration of the target substance in aportion on a boundary surface of an object increases with respect to theconcentration thereof in the surrounding portion, specifically, ischemical adsorption based on covalent bond/coordinate bond. When thetarget substance is irradiated with the light L1 of the first wavelength(incident light), generated scattered light contains Raman scatteredlight L of a wavelength different from the first wavelength of the lightL1 (see FIG. 1). The wavelength of the Raman scattered light Lcorresponds to specific vibration energy according to the structure ofthe target substance. Measuring the wavelength of the Raman scatteredlight L therefore allows identification of the target substance. Thetarget substance is, for example, acetone or ethanol.

The first structural members 14, when they adsorb the target substance,generate charge transfer (CT) resonance in response to the light L1 ofthe first wavelength. FIG. 3 describes the charge transfer resonance. InFIG. 3, Evac represents the vacuum level, and Φ represents the workfunction of each of the first structural members 14.

When the surface of each of the first structural members 14 (Al, forexample) adsorbs a target substance (acetone, for example), themolecular orbital of acetone and the electronic orbital of Al interactwith each other to produce an Al-acetone complex. At this point, a Fermilevel (E_(F)) is present in the Al, and a difference in energy (hv_(CT))ranging from 1 to 4 eV is created between the Fermi level in the Al anda HOMO (highest occupied molecular orbital) level or a LUMO (lowestunoccupied molecular orbital) level in an acetone molecule. When theAl-acetone complex is irradiated with light having energy ranging from 1to 4 eV (hv_(CT)), charge transfer optical absorption (CT absorption)occurs in the Al-acetone complex, followed by excitation between theHOMO level and the Fermi level or between the Fermi level and the LUMOlevel, which is called “charge transfer (CT) resonance (charge transfertransition).” The energy band where the CT resonance occurs is called aCT level, which can be identified by measuring an electron spectrum.

The Al-acetone complex that generates the CT resonance provides aresonance Raman effect. The “resonance Raman effect” is a phenomenon inwhich a Raman scattering cross-sectional area increases by a factor of10² to 10⁴ when the excitation wavelength is a wavelength having energycorresponding to an electronic transition absorption band. When a hybridorbital level formed when a metal chemically adsorbs a molecule has anenergy-wise width as described above, the molecule is more likely totransition to an excited state, resulting in enhancement of Ramanscattered light, which is called a “chemical enhancement effect.” Thechemical enhancement effect is provided only when the surface of any ofthe first structural members 14 adsorbs a target substance.

The second structural members 16 are provided on the substrate 12, asshown in FIG. 2. The shape of the second structural members 16 is notlimited to a specific shape, but the size of the second structuralmembers 16 (the size in a plan view, the diameter in a case where theshape in a plan view is a circle) is smaller than or equal to the firstwavelength of the light L1 emitted from the light source 20. The secondstructural members 16 may have a cylindrical shape. The size of thesecond structural members 16 is greater than or equal to 40 nm but lessthan or equal to 75 nm and is more preferably 50 nm. The secondstructural members 16 preferably have a thickness, for example, greaterthan or equal to 5 nm but less than or equal to 100 nm. The secondstructural members 16 are provided in a plurality of positions. In theexample shown in FIG. 2, the plurality of second structural members 16are periodically disposed. The spacing (e.g., distance) between adjacentsecond structural members 16 is, for example, greater than or equal to 1nm but less than or equal to 100 nm.

The second structural members 16 are made of a metal that is differentfrom the material (e.g., the metal material) of the first structuralmembers 14. Preferably, the second structural members 16 are made of,for example, Ag, Au, or Al. For example, the first structural members 14are made of Al, and the second structural members 16 are made of Ag.

The second structural members 16 generate surface plasmon resonance(SPR) in response to the light L1 of the first wavelength emitted fromthe light source 20. Specifically, the second structural members 16generate localized surface plasmon resonance (LSPR) in response to thelight L1 of the first wavelength. “LSPR” is a phenomenon in which whenlight is incident on a metal microstructure smaller than or equal to thewavelength of the light (second structural members 16), the electricfield component of the light collectively vibrates free electronspresent in the metal so that a localized electric field is induced in aspace outside the metal. The localized electric field can enhance Ramanscattered light. The enhancement of Raman scattered light under anelectric field induced by SPR as described above is called an “electricfield enhancement effect.”

The second structural members 16 are disposed so that they are spacedapart from the first structural members 14 by a spacing D, which is 5 nmor less. The spacing D may be zero (D=0). That is, the second structuralmembers 16 may be provided so that they are in contact with the firststructural members 14.

The sentence “The second structural members are disposed so that theyare spaced apart from the first structural members by a spacing, whichis 5 nm or less” means that each of the second structural members 16 isspaced apart from the first structural member 14 that is closest theretoby 5 nm or less. That is, the spacing between a second structuralmembers 16 a and a first structural members 14 a is 5 nm or less asshown in FIG. 2, but the spacing between the second structural member 16a and a first structural member 14 b may not be 5 nm or less.

When the spacing D between the second structural members 16 and thefirst structural members 14 is set at 5 nm or less, synergy between theelectric field enhancement effect and the chemical enhancement effectallows the optical device 10 to provide a surface enhanced Ramanscattering spectroscopy (SERS) effect. The intensity of the Ramanscattered light L_(RAM) can therefore be increased. It is noted that themagnitude of a localized electric field (hotsite) induced by LSPR ismaximized on the surface of each of the second structural members 16 andexponentially decreases with distance from the surface of the secondstructural member 16. When the spacing between the first structuralmembers and the second structural members is greater than 5 nm, nosynergy between the electric field enhancement effect and the chemicalenhancement effect can be provided. In this case, the intensity of theRaman scattered light L_(RAM) cannot be sufficiently increased.

1.2. Light Source

The light source 20 emits the light L1 of the first wavelength, as shownin FIG. 1. The light source 20 is, for example, a semiconductor laser,and the light L1 of the first wavelength is laser light. The firstwavelength of the light L1 is not limited to a specific value and is,for example, greater than or equal to 500 nm but less than or equal to700 nm and is more preferably 632 nm. The light L1 of the firstwavelength causes a complex of the first structural members 14 and thetarget substance (Al-acetone complex, for example) that is produced whenthe first structural members 14 adsorbs the target substance to generateCT resonance. Further, the light L1 of the first wavelength causes thesecond structural members 16 to generate LSPR.

1.3. Optical Detector

The optical detector 30 receives light radiated from the optical device10. Specifically, the optical detector 30 receives the Raman scatteredlight (SERS light) L_(RAM) radiated from the optical device 10 (enhancedby optical device 10). The optical detector 30 may be formed, forexample, of a CCD (charge coupled device), a photomultiplier, aphotodiode, or an imaging plate.

1.4. Specific Configuration of Raman Spectroscopic Apparatus

A specific configuration of the Raman spectroscopic apparatus 100 willbe described. FIG. 4 diagrammatically shows a specific configuration ofthe Raman spectroscopic apparatus 100 according to the presentembodiment.

The Raman spectroscopic apparatus 100 includes a gas specimen holder110, a detection section 120, a controller 130, an enclosure 140, whichaccommodates the detection section 120 and the controller 130, as shownin FIG. 4.

The gas specimen holder 110 includes the optical device 10, a cover 112,which covers the optical device 10, a suction channel 114, and adischarge channel 116. The detection section 120 includes the lightsource 20, lenses 122 a, 122 b, 122 c, and 122 d, a half-silvered mirror124, and the optical detector 30. The controller 130 includes adetection controller 132, which processes a detection signal from theoptical detector 30 to control the detection section 120, and anelectric power controller 134, which controls (supplies) electric powerfor the light source 20 and other components. The controller 130 may beelectrically connected to connection sections 136, which connects thecontroller 130 to an external apparatus, as shown in FIG. 4.

In the Raman spectroscopic apparatus 100, when a suction mechanism 117provided in the discharge channel 116 is operated, the pressure in thesuction channel 114 and the discharge channel 116 goes negative, wherebya gas specimen containing a target substance to be detected is suckedthrough a suction port 113. A dust removal filter 115 is provided at thesuction port 113 and can remove relatively large dust, part of watervapor, and other unwanted substances. The gas specimen passes throughthe suction channel 114, a portion in the vicinity of the optical device10, and the discharge channel 116 and is discharged through a dischargeport 118. When the gas specimen passes through the portion in thevicinity of the optical device 10, the target substance is adsorbed bythe surface of the optical device 10 and detected by the optical device10.

The suction channel 114 and the discharge channel 116 are so shaped thatno external light is incident on the optical device 10. The shapeprevents light that generates noise that is not related to Ramanscattered light from entering, whereby a signal having an improved S/Nratio can be produced. The channels 114 and 116 are, for example, madeof a material that suppresses light reflection and so colored that lightreflection is suppressed.

Further, the suction channel 114 and the discharge channel 116 are soshaped that fluid resistance acting on the gas specimen decreases, whichallows highly sensitive detection. For example, when the channels 114and 116 are so shaped that they have a minimum number of angled portionsand hence have a smooth shape, few angled portions block the gapspecimen. The suction mechanism 117 is, for example, a fan motor or apump that provides a static pressure and a flow rate according tochannel resistance.

In the Raman spectroscopic apparatus 100, the optical device 10 isirradiated with the light from the single-wavelength light source (laserlight source) 20. The light emitted from the light source 20 iscollected by the lens 122 a, travels via the half-silvered mirror 124and the lens 122 b, and is incident on the optical device 10. Theoptical device 10 then radiates SERS light, which passes through thelens 122 b, the half-silvered mirror 124, and the lenses 122 c and 122d, and reaches the optical detector 30. Since the SERS light containsRayleigh light of the same wavelength as the wavelength of the incidentlight from the light source 20, a filter 126 is provided in the opticaldetector 30 and removes the Rayleigh light. The light from which theRayleigh light has been removed is received by a light reception device128 via a spectrometer 127 in the optical detector 30.

The spectrometer 127 in the optical detector 30 is formed, for example,of an etalon using Fabry-Perot resonance and can change the wavelengthband of light that the spectrometer 127 transmits. The light receptiondevice 128 in the optical detector 30 provides a Raman spectrum specificto the target substance, and the resultant Raman spectrum can becompared with data held in advance for detection of the intensity of asignal from the target substance.

The Raman spectroscopic apparatus 100 is not limited to theconfiguration described above and may be any other apparatus thatincludes the optical device 10, the light source 20, and the opticaldetector 30 and can cause the optical device 10 to adsorb a targetsubstance and acquire the resultant Raman scattered light.

The Raman spectroscopic apparatus 100, for example, has the followingcharacteristics.

In the Raman spectroscopic apparatus 100, the optical device 10 includesthe first structural members 14, which adsorb a target substance andgenerate charge transfer resonance in response to the light L1 of thefirst wavelength, and the second structural members 16, which aredisposed so that they are spaced apart from the first structural members14 by the spacing D, which is 5 nm or less, and generate surface plasmonresonance in response to the light L1 of the first wavelength. The firststructural members 14 are made of a metal, and the second structuralmembers 16 are made of a metal different from the material of the firststructural members 14. In the thus configured Raman spectroscopicapparatus 100, appropriate selection of the materials of the firststructural members 14 and the second structural members 16 in accordancewith a target substance allows the light L1 of the first wavelength toexert a chemical enhancement effect based on CT resonance and anelectric field enhancement effect based on LSPR. More specifically, theRaman spectroscopic apparatus 100 can provide the chemical enhancementeffect even when the target substance is acetone or ethanol, which aRaman spectroscopic apparatus including an optical device havingperiodically arranged metal particles made of, for example, Ag cannotdetect in a highly sensitive manner (cannot provide chemical enhancementeffect), and the resultant synergy between the electric fieldenhancement effect and the chemical enhancement effect allows a SERSeffect to be provided (see Experimental Examples that will be describedlater for details). As a result, the Raman spectroscopic apparatus 100can increase the intensity of the Raman scattered light L and can hencedetect the Raman scattered light from the target substance in a highlysensitive manner. Specifically, the Raman spectroscopic apparatus 100can detect acetone and ethanol at a resolution of ppb (parts perbillion).

In the Raman spectroscopic apparatus 100, the second structural members16 are made of Ag, Au, or Al. Each of Ag, Au, and Al is a metal having adielectric constant with a small imaginary part in the visiblewavelength range and can hence enhance the electric field enhancementeffect.

In the Raman spectroscopic apparatus 100, the target substance isacetone or ethanol. The Raman spectroscopic apparatus 100 can alsodetect a molecule not containing an N atom, such as acetone and ethanol,in a highly sensitive manner.

In the Raman spectroscopic apparatus 100, the target substance isacetone. The first wavelength is greater than or equal to 500 nm butless than or equal to 700 nm, and the size of the second structuralmembers is greater than or equal to 40 nm but less than or equal to 75nm. The Raman spectroscopic apparatus 100 therefore allows thewavelength band where the electric field enhancement effect can beenhanced and the wavelength band where the chemical enhancement effectcan be enhanced to coincide with each other. As a result, synergybetween the electric field enhancement effect and the chemicalenhancement effect can be more reliably obtained (see ExperimentalExamples that will be described later for details).

As described above, in the Raman spectroscopic apparatus 100, thematerial of the second structural members 16 can be so selected inaccordance with the wavelength band where the CT level of a targetsubstance is present that the wavelength band where the electric fieldenhancement effect can be enhanced and the wavelength band where thechemical enhancement effect can be enhanced coincide with each other.For example, when the wavelength band where the CT level is presentranges from 300 to 400 nm, Al is used. When the wavelength band rangesfrom 400 to 700 nm, Ag is used. When the wavelength band is 700 nm andgreater, Au is used.

2. METHOD FOR MANUFACTURING RAMAN SPECTROSCOPIC APPARATUS

A method for manufacturing the Raman spectroscopic apparatus 100according to the present embodiment will be described next.

The optical device 10 is formed based, for example, on a nanospherelithography (NSL) technology. Preferably, polystyrene (PS) beads eachhaving a diameter of about 350 nm are mixed with ethanol, and thebead-containing ethanol is gently dripped into a beaker that containspure water. The dripped ethanol is mixed with the pure water layer,whereas the PS beads spread over the gas-liquid interface. The substrate12 is then gently placed on the gas-liquid interface to lift up the PSbeads. A PS-filled substrate having a PS bead monolayer in which the PSbeads are arranged in a closest-packed pattern is thus produced.

The PS-filled substrate then undergoes AR-NSL (angle resolved nanospherelithography). “AR-NSL” is a metal evaporation method performed at leasttwice at different metal evaporation angles by using the PS beads in thePS-filled substrate as a mask. For example, the first structural members14 are formed by performing oblique evaporation in a direction inclinedby 20° to a normal to the upper surface of the substrate 12 toward oneside of the normal. The second structural members 16 are then formed byperforming oblique evaporation in a direction inclined by 20° to thenormal to the upper surface of the substrate 12 toward the other side ofthe normal.

The PS beads are then removed. The PS beads are removed, for example, bycausing them to undergo ultrasonic processing in water.

The optical device 10 can be formed by carrying out the steps describedabove.

The optical device 10, the light source 20, and the optical detector 30are then placed in predetermined positions. The Raman spectroscopicapparatus 100 can thus be manufactured.

3. RAMAN SPECTROSCOPIC METHOD

A Raman spectroscopic method according to the present embodiment will bedescribed next. In the Raman spectroscopic method according to thepresent embodiment, the optical device that has adsorbed a targetsubstance is irradiated with the light of the first wavelength, andlight radiated from the optical device is received, followed by analysisof the target substance. Preferably, the Raman spectroscopic methodaccording to the present embodiment is performed by using the Ramanspectroscopic apparatus 100. The above description of the Ramanspectroscopic apparatus 100 can therefore be applied to the descriptionof the Raman spectroscopic method according to the present embodiment.No detailed description of the Raman spectroscopic method according tothe present embodiment will therefore be made.

4. EXPERIMENTAL EXAMPLES

Experimental Examples will be shown below for more specific descriptionof the invention. The following Experimental Examples are not intendedto limit the invention in any sense.

4.1. First Experiment 4.1.1. CT Level Measurement

1. Measurement System

Surface differential reflection spectroscopy (SDRS) was used to measurea CT level in a case where a metal (first structural members) adsorbs atarget substance in an atmospheric environment.

FIG. 5 diagrammatically shows an SDRS measurement system 1000. Lightemitted from a white light source 1002 is parallelized by a lens 1004and passes through a polarizer 1006, which converts the light intoP-polarized light, as shown in FIG. 5. A beam splitter 1008 splits thelight from the white light source 1002 into two, and one of the splitlight fluxes is used as reference light by a spectrometer 1010 tomeasure fluctuation of the intensity of the light from the light source.The other one of the split light fluxes is used to measure a specimensubstrate S. The specimen substrate S is placed in a sealed cell 1012made of transparent glass, and light reflected off the surface of thespecimen substrate S passes through a pinhole 1014 and a lens 1016 andis detected by a spectrometer 1018, where the light undergoes aspectroscopic process. A tube 1024 is connected to the sealed cell 1012and has an open/close cock 1022, which allows vapor of a targetsubstance to be transported from a target substance vapor generator1020.

SDRS, in which the incident light, which is P-polarized light, isallowed to be incident on the surface of the specimen substrate S atabout Brewster's angle, allows measurement of an electron spectrum ofthe metal surface at atomic layer level sensitivity.

2. Measurement Results

In the measurement system described above, an Ag substrate was used asthe specimen substrate S, and a gas-state target substance was exposedto the Ag surface for measurement of a change in the electron spectrum(SDRS spectrum) before and after the exposure. FIG. 6 shows SDRS spectrabefore and after pyridine vapor is exposed to the Ag surface. In FIG. 6,the horizontal axis represents the wavelength of the incident lightincident on the Ag surface, and the vertical axis represents ΔR/Rcomputed based on the following Expression (1).ΔR/R=(R−R ₀)/R ₀  (1)

In Expression (1), R₀ represents the reflectance before the targetsubstance is exposed, and R represents the reflectance after the targetsubstance is exposed.

That is, a negative ΔR/R value means that the specimen substrate S hasabsorbed the target substance. R₀ can be lowered by causing the incidentlight to be incident at Brewster's angle. The sensitivity can thus beincreased.

The SDRS spectrum after the exposure of the pyridine has two absorptionbands, unlike the SDRS spectrum before the exposure, as shown in FIG. 6.One of the two absorption bands ranges from 400 to 550 nm, and the otherranges from 600 to 1000 nm. These absorption bands show opticalabsorption corresponding to CT levels of an Ag-pyridine complex producedwhen Ag adsorbs pyridine.

FIG. 7 shows SDRS spectra before and after acetic acid vapor is exposedto the Ag surface. The SDRS spectrum after the exposure of the aceticacid, specifically, a portion of the spectrum in the range from 440 to1000 nm has an absorption band corresponding to a CT level, as shown inFIG. 7.

FIG. 8 shows SDRS spectra before and after acetone vapor is exposed tothe Ag surface. FIG. 9 shows SDRS spectra before and after ethanol vaporis exposed to the Ag surface.

The SDRS spectra of the acetone and the ethanol hardly change before andafter the exposure, unlike the pyridine and the acetic acid, as shown inFIGS. 8 and 9, which means that no CT level is formed.

4.1.2. SERS Intensity Measurement

The Ag substrate was then placed in a gas-state target substanceatmosphere for SERS intensity measurement. Specifically, the measurementsystem shown in FIG. 1 was used, in which the first wavelength of thelight L1 (excitation wavelength) emitted from the light source 20 wasset at 632 nm, and L was received by the optical detector 30 for SERSintensity (SERS spectrum) measurement.

FIG. 10 shows SERS spectra in gas-state pyridine, acetic acid, acetone,and ethanol atmospheres. The pyridine (see FIG. 6) and the acetic acid(see FIG. 7), in each of which a CT level was present at 632 nm,provided very strong signals, as shown in FIG. 10. On the other hand,the acetone (see FIG. 8) and the ethanol (see FIG. 9), in each of whichno CT level was present at 632 nm, hardly provided signals, as shown inFIG. 10.

The vertical axis of FIG. 10 represents SERS relative intensity insteadof absolute intensity. That is, in the example shown in FIG. 10, theAg-pyridine complex has peaks higher than those for the Ag-acetic acidcomplex, which does not necessarily mean that the SERS intensityprovided by the Ag-pyridine complex is greater than the SERS intensityprovided by the Ag-acetic acid complex. This holds true for FIG. 13,which will be described later.

FIG. 11 shows a graph illustrating the relationship between theexcitation wavelength and the SERS intensity in the gas-state aceticacid atmosphere. Comparison of FIG. 11 with FIG. 7 shows that thebehavior of ΔR/R substantially coincides with the behavior of the SERSintensity. That is, in the wavelength band where ΔR/R has a largeabsolute value in FIG. 7, the SERS intensity has large values in FIG.11. That is, it is shown that presence or absence of a CT level(presence or absence of chemical enhancement effect) results in adistinct difference in the SERS intensity.

4.2. Second Experiment 4.2.1. CT Level Measurement

An experiment for providing the chemical enhancement effect wasperformed in a case where acetone was used as the target substance.

An Al substrate (Ag substrate on which an Al film is formed to athickness of about 1 nm) was used in place of the Ag substrate used inthe first experiment for CT level measurement in the SDRS system. FIG.12 shows spectra before and after acetone vapor is exposed to the Alsurface.

The SDRS spectrum after the exposure shows that an absorption bandcorresponding to a CT level is present across the visible range (from500 to 700 nm, in particular), as shown in FIG. 12. That is, it can besaid that acetone, when adsorbed by Al, generates CT resonance.

4.2.2. SERS Intensity Measurement

The Al substrate was then placed in the gas-state acetone atmosphere forSERS intensity measurement. FIG. 13 shows a SERS spectrum in thegas-state acetone atmosphere in a case where the excitation wavelengthis 632 nm. FIG. 13 further shows the SERS spectrum in the case where theAg substrate was placed in the gas-state acetone atmosphere forcomparison purposes.

In the Al substrate measurement, a distinct spectrum was detected,unlike the Ag substrate measurement, as shown in FIG. 13. That is, it isshown that even when the target substance is acetone, using firststructural members made of Al allows the SERS intensity to be increasedby the chemical enhancement effect based on CT resonance.

4.3. Third Experiment

An experiment for investigating an optimum size (diameter, for example)of Ag particles (second structural members 16) was performed. A specimen(optical device) used in the present experiment was a glass substrate(substrate 12) on which Al particles (first structural members 14) andAg particles (second structural members 16) were formed by using the NSLtechnology and the AR-NSL method described above. FIG. 14 is a SEMphotograph of the specimen used in the present experiment. The size(size in plan view) of the Al particles was set at 20 nm. The size (sizein plan view) of the Ag particles was changed among the following threelevels: 50 nm; 75 nm; and 100 nm.

FIG. 15 shows graphs illustrating the relationship between theexcitation wavelength and the optical density of the specimen producedas described above. The optical density along the vertical axis of FIG.15 is a value based on LSPR, and the greater the optical density, thegreater the electric field enhancement effect provided by LSPR of the Agparticles. FIG. 15 shows that the optical density changes with theexcitation wavelength.

FIG. 12 shows that, to allow the Al-acetone complex to generate CTresonance, the excitation wavelength is preferably set at a valuegreater than or equal to 500 nm but less than or equal to 700 nm.Therefore, setting the diameter of the Ag particles at a value greaterthan or equal to 40 nm but less than or equal to 75 nm and morepreferably a value equal to 50 nm allows the wavelength band where theelectric field enhancement effect can be enhanced based on LSPR and thewavelength band where the chemical enhancement effect can be enhancedbased on CT resonance to coincide with each other, as shown in FIG. 15.As a result, synergy between the electric field enhancement effect andthe chemical enhancement effect can be more reliably provided.Specifically, synergy between the electric field enhancement effect andthe chemical enhancement effect at the excitation wavelength of 632 nmallows highly sensitive detection of acetone.

5. VARIATIONS OF RAMAN SPECTROSCOPIC APPARATUS

5.1. First Variation

A Raman spectroscopic apparatus according to a first variation of thepresent embodiment will be described next with reference to thedrawings. FIG. 16 is a cross-sectional view diagrammatically showing theoptical device 10 of a Raman spectroscopic apparatus 200 according tothe first variation of the present embodiment.

The Raman spectroscopic apparatus 200 according to the first variationof the present embodiment will be described below about points differentfrom those in the Raman spectroscopic apparatus 100 according to thepresent embodiment, and the same points will not be described. The sameholds true for the Raman spectroscopic apparatus according to thesecond, third, and fourth variations, which will be described below.

In the Raman spectroscopic apparatus 100, the second structural members16 are disposed so that they are spaced apart from the first structuralmembers 14 by the spacing of 5 nm or less, as shown in FIG. 2. Incontrast, in the Raman spectroscopic apparatus 200, a first structuralmember 14 is disposed so that it coats (e.g., entirely surrounds orencases a free surface of) second structural members 16, as shown inFIG. 16. That is, the first structural member 14 is provided so that itis in contact with the second structural members 16. In the exampleshown in FIG. 16, the first structural member 14 is also provided on thesubstrate 12 (upper surface of substrate 12).

In the example shown in FIG. 16, the first structural member 14completely covers the surfaces of the second structural members 16 notin contact with the substrate 12. However, part of the surfaces of thesecond structural members 16 may be exposed through the first structuralmember 14 as long as the first structural member 14 can provide achemical enhancement effect.

A method for manufacturing the optical device 10 of the Ramanspectroscopic apparatus 200 will be described. The second structuralmembers 16 are first formed on the substrate 12. The second structuralmembers 16 are formed, for example, by forming an Ag film in a vacuumevaporation process at a film formation speed ranging from 0.1 to 1angstrom per second. Forming the Ag film under the conditions describedabove allows formation of an island-shaped Ag structure in aself-assembled manner, as illustrated in the SEM photograph shown inFIG. 17. The first structural member 14 is next formed on the secondstructural members 16 and the substrate 12. The first structural member14 is formed, for example, by forming an Al film in a vacuum evaporationprocess. The optical device 10 can be manufactured by carrying out thesteps described above.

In the Raman spectroscopic apparatus 200, the first structural member 14preferably has a thickness (specifically, film thickness of firststructural member 14 on substrate 12) T less than or equal to 1 nm, asshown in FIG. 16. The thus sized first structural member 14 allowsenhancement of the electric field enhancement effect based on LSPR. FIG.18 shows graphs illustrating the relationship between the thickness ofthe first structural member 14 (Al) and a relative SERS intensity (SERSintensity normalized with respect to SERS intensity in a case where Althickness is zero). FIG. 18 shows calculated plots from an FDTD(finite-difference time-domain) calculation simulation and actualmeasurements for the optical device formed by using the manufacturingmethod described above.

The relative SERS intensity decreases as the Al thickness increases andbecomes extremely small when the Al thickness becomes greater than 1 nm,as shown in FIG. 18. An estimated reason for this is that when the Althickness is large, the Ag particles (second structural members 16) areelectrically connected to each other, which prevents localization offree electrons under LSPR.

The Raman spectroscopic apparatus 200 differs from the Ramanspectroscopic apparatus 100 in that the optical device 10 can be formedin simpler manufacturing steps. Further, in the Raman spectroscopicapparatus 200, setting the thickness of the first structural member 14at 1 nm or less allows enhancement of the electric field enhancementeffect.

5.2. Second Variation

A Raman spectroscopic apparatus according to a second variation of thepresent embodiment will be described next with reference to thedrawings. FIG. 19 is a cross-sectional view diagrammatically showing theoptical device 10 of a Raman spectroscopic apparatus 300 according tothe second variation of the present embodiment.

In the Raman spectroscopic apparatus 100, the second structural members16 are disposed so that they are spaced apart from the first structuralmembers 14 by the spacing of 5 nm or less, as shown in FIG. 2. Incontrast, in the Raman spectroscopic apparatus 300, the first structuralmembers 14 are disposed so that they coat (e.g., entirely surround orencases a free surface of) the second structural members 16 and theplurality of first structural members 14 are spaced apart from eachother, as shown in FIG. 19. That is, the first structural members 14 areprovided so that they are in contact with the second structural members16. In the example shown in FIG. 19, part of the upper surface of thesubstrate 12 is exposed. The first structural members 14 may be providedso that they are spaced apart from (not in contact with) the substrate12.

In the example shown in FIG. 19, the first structural members 14completely cover the surfaces of the second structural members 16 not incontact with the substrate 12. However, part of the surfaces of thesecond structural members 16 may be exposed through the first structuralmembers 14 as long as the first structural members 14 can provide achemical enhancement effect.

A method for manufacturing the optical device 10 of the Ramanspectroscopic apparatus 300 will be described with reference to thedrawings. FIGS. 20A and 20B to 22A and 20B describe steps ofmanufacturing the optical device 10 of the Raman spectroscopic apparatus300 according to the second variation of the present embodiment. FIGS.20A, 21A, and 22A are perspective views diagrammatically showing themanufacturing steps, and FIGS. 20B, 21B, and 22B are SEM photographs(SEM photographs in plan view) showing the manufacturing steps.

A resist 302 is applied onto the substrate 12 (glass substrate), asshown in FIG. 20A. A two-dimensional array of nano-dots 304, each ofwhich has, for example, a diameter of about 100 nm and which arearranged, for example, at a period of 140 nm, is then formed in theresist 302 in a lithography process using an electron beam drawingmethod.

Thereafter, for example, an Ag film 306, which will form the secondstructural members 16, is formed to a thickness of about 30 nm, followedby formation of an Al film 308, which will form the first structuralmembers 14, as shown in FIG. 21A. The Ag film 306 and the Al film 308are formed, for example, in a vacuum evaporation process.

The resist 302 is lifted off by using a separation liquid, as shown inFIG. 22A. As a result, the Ag film 306 and the Al film 308, which willform the structural members 14 and 16 respectively, can be formed on thesubstrate 12.

The optical device 10 of the Raman spectroscopic apparatus 300 can bemanufactured by carrying out the steps described above.

FIG. 23 shows graphs illustrating the relationship between the thicknessof the first structural members 14 (Al) and the relative SERS intensity(SERS intensity normalized with respect to SERS intensity in a casewhere Al thickness is zero) in the optical device formed by using themanufacturing method described above. The plots shown in FIG. 23 werecalculated by using the FDTD calculation simulation. FIG. 23 furthershows plots of the FDTD results shown in FIG. 18 for comparisonpurposes. That is, FIG. 23 shows plots corresponding to the opticaldevice 10 of the Raman spectroscopic apparatus 200 and plotscorresponding to the optical device 10 of the Raman spectroscopicapparatus 300.

FIG. 23 shows that the Raman spectroscopic apparatus 300 differs fromthe Raman spectroscopic apparatus 200 in that increasing the Althickness does not result in a decrease in the relative SERS intensity.The reason for this is that in the Raman spectroscopic apparatus 300, inwhich the Al particles (first structural members 14) are notcontinuously connected to each other, conduction between the Agparticles (second structural members 16) can be prevented.

The Raman spectroscopic apparatus 300 differs from the Ramanspectroscopic apparatus 100 in that the optical device 10 can be formedin simpler manufacturing steps and differs from the Raman spectroscopicapparatus 200 in that the electric field enhancement effect can beenhanced irrespective of the thickness of the first structural members14.

5.3. Third Variation

A Raman spectroscopic apparatus according to a third variation of thepresent embodiment will be described next.

In the Raman spectroscopic apparatus 100 according to the firstvariation (see FIG. 2), the first structural members 14 are made of ametal. In contrast, in the Raman spectroscopic apparatus according tothe third variation, the first structural members 14 are made of asemiconductor. Preferably, the first structural members 14 are made ofsilicon.

In the Raman spectroscopic apparatus according to the third variation,the first structural members 14 can be formed by forming a silicon filmin a sputtering process and then patterning the silicon film inphotolithography and etching processes.

FIG. 24 shows SDRS spectra before and after acetone vapor is exposed tothe Si surface. FIG. 24 shows that after the exposure of acetone, a CTlevel is present over the visible region. It is believed that Si canchemically adsorb acetone and an Si-acetone complex has a hybrid orbitalof the electronic orbital of Si and the molecular orbital of acetone asshown in FIG. 25. It is believed that the result shown in FIG. 24 wasobtained based on the assumption described above.

The Raman spectroscopic apparatus according to the third variation isunlikely to corrode due to oxygen, sulfur, and other substances in theair, unlike the Raman spectroscopic apparatus 100. That is, the Ramanspectroscopic apparatus according to the third variation is lessaffected by oxygen, sulfur, and other substances in the air than theRaman spectroscopic apparatus 100 and is hence unlikely to deteriorate.

5.4. Fourth Variation

A Raman spectroscopic apparatus according to a fourth variation of thepresent embodiment will be described next. FIG. 26 diagrammaticallyshows a Raman spectroscopic apparatus 400 according to the fourthvariation of the present embodiment.

The Raman spectroscopic apparatus 400 includes a light source 420, asshown in FIG. 26. The light source 420 irradiates a target substancewith light L2 of a second wavelength having energy corresponding to thedifference in energy between the ground state and a minimally excitedstate of the target substance. That is, the light source 420 irradiatesthe target substance with the light L2 of the second wavelength havingenergy corresponding to the difference in energy between the HOMO leveland the LUMO level. The second wavelength of the light L2 differs fromthe first wavelength of the light L1.

FIG. 27 describes the structure of an acetone molecule, which is thetarget substance. Ketones, such as acetone, can have a keto formstructure and an enol form structure and typically exists in the ketoform, which is stable, and the proportion of the enol form, which ishighly reactive, is 0.1% or lower.

FIG. 28 shows an absorption spectrum of acetone gas alone in avisible-ultraviolet region. An absorption wavelength of acetone ispresent at a wavelength close to 275 nm, as shown in FIG. 28. Thewavelength corresponds to the difference in energy between the HOMOlevel and the LUMO level of acetone.

In the Raman spectroscopic apparatus 400, the light source 420 canirradiate acetone with the light L2 of the wavelength of 275 nm tochange the acetone from the keto form to the enol form shown in FIG. 27.That is, in the Raman spectroscopic apparatus 400, the light L2 of thesecond wavelength can excite acetone from its ground state to itsminimally excited state, whereby the acetone can be more reactive.

FIG. 29 shows SDRS spectra before and after acetone vapor is exposed toa Cu surface. Simply exposing acetone to the Cu surface provides no CTlevel, as shown in FIG. 29. FIG. 29, however, shows that irradiation ofthe acetone atmosphere with 275-nm DUV (deep ultraviolet) light providesa CT level in a wavelength region ranging from 400 to 500 nm. The reasonfor this is that the acetone irradiated with the DUV light is excited toits minimally excited state, which encourages the reaction in which theCu surface adsorbs the acetone.

In the Raman spectroscopic apparatus 400, in which the target substanceis irradiated with the light L2 of the second wavelength having energycorresponding to the difference in energy between the HOMO level and theLUMO level, the reaction in which the first structural members 14 adsorbthe target substance is encouraged, whereby the chemical enhancementeffect can be enhanced.

6. ELECTRONIC APPARATUS

An electronic apparatus 500 according to the present embodiment will bedescribed next with reference to the drawings. FIG. 30 diagrammaticallyshows the electronic apparatus 500 according to the present embodiment.The electronic apparatus 500 can be equipped with any of the Ramanspectroscopic apparatus according to the embodiment of the invention andthe variations thereof. A description will be made of the electronicapparatus 500 including the Raman spectroscopic apparatus 100 as theRaman spectroscopic apparatus according to the embodiment of theinvention and the variations thereof.

The electronic apparatus 500 includes the Raman spectroscopic apparatus100, a computation unit 510, which computes healthcare information basedon detected information from the optical detector 30, a storage unit520, which stores the health care information, and a display unit 530,which displays the health care information, as shown in FIG. 30.

The computation unit 510 is, for example, a personal computer or apersonal digital assistant (PDA) and receives detected information (suchas signal) transmitted from the optical detector 30. The computationunit 510 computes health care information based on the detectedinformation from the optical detector 30. The computed health careinformation is stored in the storage unit 520.

The storage unit 520 is, for example, a semiconductor memory or a harddisk drive and may be integrated with the computation unit 510. Thehealth care information stored in the storage unit 520 is transmitted tothe display unit 530.

The display unit 530 is formed, for example, of a display panel (such asliquid crystal monitor), a printer, a light emitter, a loudspeaker orthe like. The display unit 530 displays or issues, based, for example,on the health care information computed by the computation unit 510,information that allows a user to recognize the contents of the healthcare information.

Examples of the health care information may include information onwhether or not there is at least one type of biological substanceselected from the group consisting of bacteria, viruses, proteins,nucleic acids, and antigens and antibodies or at least one type ofcompound selected from inorganic molecules and organic molecules orinformation on the amount thereof.

The computation unit 510 and the storage unit 520 may be integrated withthe controller 130 shown in FIG. 4.

The electronic apparatus 500 includes the Raman spectroscopic apparatus100, which is capable of detecting Raman scattered light from a targetsubstance in a highly sensitive manner. The electronic apparatus 500 cantherefore readily detect a trace quantity of substance and providehighly precise health care information.

The embodiment and the variations described above are examples, and theinvention is not limited thereto. For example, the embodiment and thevariations can be combined with each other as appropriate.

The scope of the invention encompasses substantially the sameconfiguration as the configuration described in the embodiment (forexample, a configuration having the same function, using the samemethod, and providing the same result or a configuration having the samepurpose and providing the same effect). Further, the scope of theinvention encompasses a configuration in which an inessential portion ofthe configuration described in the above embodiment is replaced.Moreover, the scope of the invention encompasses a configuration thatprovides the same advantageous effect as that provided by theconfiguration described in the embodiment or a configuration that canachieve the same purpose as that achieved by the configuration describedin the embodiment. Further, the scope of the invention encompasses aconfiguration in which a known technology is added to the configurationdescribed in the embodiment.

The entire disclosure of Japanese Patent Application No. 2013-183944filed Sep. 5, 2013 is expressly incorporated by reference herein.

What is claimed is:
 1. A Raman spectroscopic apparatus comprising: alight source that emits first wavelength light; an optical device thatadsorbs a substance under analysis and is irradiated with the firstwavelength light; and an optical detector that receives radiated lightfrom the optical device irradiated with the first wavelength light,wherein the optical device includes: a first structural member thatgenerates charge transfer resonance in response to irradiation with thefirst wavelength light, and a second structural member that is less thanor equal to 5 nm from the first structural member and generates surfaceplasmon resonance in response to irradiation with the first wavelengthlight, the first structural member is one of a first metal or asemiconductor, and the second structural member is a second metal thatis different from the one of the first metal or the semiconductor of thefirst structural member.
 2. The Raman spectroscopic apparatus accordingto claim 1, wherein the first structural member is coated onto thesecond structural member.
 3. The Raman spectroscopic apparatus accordingto claim 2, wherein the first structural member further comprises aplurality of first structural members provided in a plurality ofpositions, and the second structural member further comprises aplurality of second structural members provided in a plurality ofpositions spaced apart from one another.
 4. The Raman spectroscopicapparatus according to claim 3, wherein the plurality of firststructural members are spaced apart from each other.
 5. The Ramanspectroscopic apparatus according to claim 1, wherein the firststructural member has a thickness less than or equal to 1 nm.
 6. TheRaman spectroscopic apparatus according to claim 1, wherein the secondstructural member is one of Ag, Au, or Al.
 7. The Raman spectroscopicapparatus according to claim 1, wherein the substance under analysis isone of acetone or ethanol.
 8. The Raman spectroscopic apparatusaccording to claim 1, wherein the substance under analysis is acetone,the first wavelength is greater than or equal to 500 nm but less than orequal to 700 nm, and a size of the second structural member in a planview is greater than or equal to 40 nm but less than or equal to 75 nm.9. The Raman spectroscopic apparatus according to claim 1, furthercomprising a second light source that irradiates the substance underanalysis with second wavelength light having energy corresponding to adifference in energy between a ground state and a minimally excitedstate of the substance under analysis.
 10. A Raman spectroscopic methodcomprising: irradiating an optical device that adsorbed a substanceunder analysis with first wavelength light, and receiving radiated lightfrom the optical device irradiated with the first wavelength light,wherein the optical device includes: a first structural member thatgenerates charge transfer resonance in response to irradiation with thefirst wavelength light, and a second structural member that is less thanor equal to 5 nm from the first structural member and generates surfaceplasmon resonance in response to irradiation with the first wavelengthlight, the first structural member is one of a first metal or asemiconductor, and the second structural member is a second metal thatis different from the one of the first metal or the semiconductor of thefirst structural member.
 11. An electronic apparatus comprising: theRaman spectroscopic apparatus according to claim 1; a computation unitthat computes information based on detected information from the opticaldetector; a storage unit that stores the information; and a display unitthat displays the information.
 12. The electronic apparatus according toclaim 11, wherein the information includes information on whether thereis at least one type of biological substance selected from the groupincluding bacteria, viruses, proteins, nucleic acids, and antigens andantibodies or at least one type of compound selected from inorganicmolecules and organic molecules or information on an amount thereof. 13.A Raman spectroscopic apparatus that analyzes a substance underanalysis, the apparatus comprising: a light source that emits firstwavelength light; an optical device that adsorbs the substance underanalysis and is irradiated with the first wavelength light; and anoptical detector that receives radiated light from the optical deviceirradiated with the first wavelength light, wherein the optical deviceincludes: a substrate, a first structural member on the substrate andgenerating charge transfer resonance in response to irradiation with thefirst wavelength light, and a second structural member on the substrate,the second structural member being less than or equal to 5 nm from thefirst structural member and generating surface plasmon resonance inresponse to irradiation with the first wavelength light, the firststructural member is one of a first metal or a semiconductor, and thesecond structural member is a second metal that is different from theone of the first metal or the semiconductor of the first structuralmember.
 14. The Raman spectroscopic apparatus according to claim 13,wherein the first structural member is coated onto the second structuralmember.
 15. The Raman spectroscopic apparatus according to claim 14,wherein the first structural member further comprises a plurality offirst structural members provided in a plurality of positions, and thesecond structural member further comprises a plurality of secondstructural members provided in a plurality of positions spaced apartfrom one another.
 16. The Raman spectroscopic apparatus according toclaim 15, wherein the plurality of first structural members are spacedapart from each other.
 17. The Raman spectroscopic apparatus accordingto claim 13, wherein the first structural member has a thickness lessthan or equal to 1 nm.
 18. The Raman spectroscopic apparatus accordingto claim 13, wherein the second structural member is one of Ag, Au, orAl.
 19. The Raman spectroscopic apparatus according to claim 13, whereinthe substance under analysis is one of acetone or ethanol.
 20. The Ramanspectroscopic apparatus according to claim 13, wherein the substanceunder analysis is acetone, the first wavelength is greater than or equalto 500 nm but less than or equal to 700 nm, and a size of the secondstructural member in plan view is greater than or equal to 40 nm butless than or equal to 75 nm.